When it comes to lubrication, oiling up something before you use it gets you a longer life. I am getting ready to put a computer into service. I'll be using two sleeve bearing fans on it. So I took pictures as I oiled one of them to prepare it to go to work. I'll be re-oiling it every three to six months.

Your choice of lubricants. The Singer oil is from Wal-Mart, The XL model train oil is from a hobby shop and the Precision Lubricator is from Radio Shack. Do not use WD-40: it is a penetrant, not a lubricant. 3-in-1 oil contains a penetrant. And EpicPie has recommended Bones Speed Cream, which looks promising.

Peel back - do not remove - the label.
Use a toothpick to pry open the rubber or plastic cap.

The open oil reservoir.

Put the oil in the reservoir. Fill it up, but leave room for the cap. You don't want to squeeze oil out when you put the cap back.

Clean off any oil from the fan surface. This will allow the label to stick firmly.

One lubricated sleeve bearing fan, ready to go to work.

As with nearly everything, the more you do this the easier and quicker it gets. Have fun!

How often do you guys lubricate your fans? I haven't lubcricated any...

I checked on my sleeve bearing top intake fan earlier this month, after two months in place. Its reservoir was still full of oil. I'll be checking every couple of months until I get some notion of how often these will need to be checked.

If you have put some sleeve bearing fans into service without lubricating them first you should take them out and lubricate them ASAP. Then probably every six months is OK. But I'm not sure, which is why I am checking.

Ball bearing fans are different, but I'm thinking some lube wouldn't hurt them when you put them into service.

Finally, some bearings are sealed - the Noctua, for one. Those you cannot lubricate.